Laundry bleaches can be classified by chemical type--chlorine bleaches and active oxygen, i.e. peroxygen, bleaches--and by physical form--solid and liquid.
The peroxygen bleaches can employ liquid hydrogen peroxide, solid organic peroxy acids, or solid inorganic peroxy salts and can offer a number of advantages. Peroxygen bleaches are safe to fabric colors and are relatively nonyellowing to white fabric. They are nondestructive to the physical strength of the fabric and impart a good handle and absorbency to the fabric.
Such peroxygen bleaches have been used for stain and soil removal in two distinct laundry settings. The first setting employs high wash temperatures, particularly over 85.degree. C. and commonly about 100.degree. C. as are often found in commercial laundries and in some European domestic laundries. At these high temperatures a peroxygen material such as hydrogen peroxide or sodium perborate or percarbonate can be added to the wash mixture and will give effective bleaching. Lower temperatures are typically found in United States domestic washing machines. Hydrogen peroxide in combination with activators has been disclosed for this application and a range of materials have been proposed as activators for peroxygen bleaches to enhance bleaching at low to moderate temperatures.
The selection of peroxygen bleach-activator combinations is a complex balancing of two contradictory characteristics. The combination must be shelf-stable and undergo a loss of no more than 10-20% of its activity over a 90 day period at 15.degree.-30.degree. C. On the other hand, the combination must be so reactive that when added to a cold water (10.degree.-30.degree. C.) laundry solution, it will react substantially in 1-2 minutes so as to be effective through most of the 10-12 minute wash period of an automatic washer cycle. Thus, a peroxygen compound-activator combination must exhibit a reaction rate in the washing machine that is 10,000 to 100,000 times as fast as the decomposition rate which is tolerable during storage. With solid or dry powder compositions, shelf stability can be achieved by mixing the solid persalt and solid activator as dry powders, and so long as they are kept dry during storage, no significant reaction or loss of activity will occur until the mixture is added to the washing machine. In high humidity environments such as often occur in laundry rooms, dry products can become damp and lose activity. When liquid hydrogen peroxide is employed as the peroxide source, it is not possible to have a dry powder product.
There have also been several proposals for liquid peroxide bleaches heretofore. However, none of these have disclosed how to incorporate activators and achieve a storage-stable product.
Barrett, Jr. in U.S. Pat. No. 3,970,575 shows a hydrogen peroxide bleach product which is acid-stabilized but which is not seen to contain any activator.
Jones in U.S. Pat. No. 3,956,159 shows a liquid bleach based on organic peroxyacids and their salts in an anhydrous organic ternary solvent.
Edwards et al in U.S. Pat. No. 3,996,152 shows a fluid product which employs a suspension of water-insoluble solid peroxygen compound, a nonstarch thickener, and an acidifier in a liquid carrier such as water. In light of the requirement that the peroxygen compound be water-insoluble, hydrogen peroxide would not be applicable to this system.
Bradley in U.S. Pat. No. 4,017,412 shows the same type of system as does Edwards et al but uses a starch thickener.
Kandathill in U.S. Pat. No. 4,238,192 shows a hydrogen peroxide-based liquid bleach. It does not appear to contain any activators but has acid to give a pH of 2.8 to 5.5 and a nitrogen compound (in particular, an amino acid) to give stability.
Lutz et al in U.S. Pat. No. 4,130,501 discloses a liquid hydrogen peroxide bleach to which has been added a surfactant and a thickening agent, again with no specific recitation of having an activator present in the mixture.
Thus, those references in the art which are directed to stable liquid peroxygen bleaches do not address the need to have activator present while those references dealing with activator systems do not address how to select or use an activator in a way which will work in a long term stable liquid bleach based on hydrogen peroxide.
It is against this background and in light of the particular problems posed by a liquid bleach which is based on hydrogen peroxide and must be storage stable on the one hand but must contain activators to give good bleaching performance at low to moderate wash temperatures that the present invention has been made.